/**
 * @var array
 *
 * @ORMColumn(type="simple_array")
 */
private $tags;

protected function configureFormFields(FormMapper $formMapper)
{
    $formMapper
        ->add('tags', 'collection');
}

protected function configureListFields(ListMapper $listMapper)
{
    $listMapper
        ->add('tags', 'array');
}